I have done extensive renovations in older homes in the Washington, DC area and we have almost always applied a new layer of drywall over the plaster and screwed through to the lath or joists behind the plaster. Your plaster will most likely continue to be a problem, if a patch job is all you do. It's a fairly simple process and will leave you with a new ceiling that will keep from cracking. I suggest you have this done by a professional, as their skill in finishing the drywall will be the difference between a job you'll love and one you'll have to live with. Good luck.